Gravel pack assemblies and frac pack assemblies are commonly used in oil field well completions. A frac pack assembly is used to stimulate well production by using liquid under high pressure pumped down a well to fracture the reservoir rock adjacent to the wellbore. Propping agents suspended in the high-pressure liquid (in hydraulic fracturing) are used to keep the fractures open, thus facilitating increased flow rates into the wellbore. Gravel pack completions are commonly used for unconsolidated reservoirs and for sand control. Gravel packs can be used in open-hole completions or inside-casing applications. An example of a typical gravel pack application involves reaming out a cavity in the reservoir and then filling the well with sorted, loose sand (referred to in the industry as gravel). This gravel pack provides a consolidated sand layer in the wellbore and next to the surrounding reservoir producing formation, thus restricting formation sand migration. A slotted or screen liner is run in the gravel pack which allows the production fluids to enter the production tubing while filtering out the surrounding gravel.
A typical gravel pack completion is illustrated in FIG. 1. FIG. 1 is a schematic representation showing a perforated wellbore annulus 2, with perforation shown extending into the zone of interest 5. Within the wellbore annulus 2 a tube 4 has been placed on which is attached a screen 6. The gravel 3 is shown packed into the perforations in the zone of interest 5 and surrounding the screen 6. The gravel 3 is an effective filter of formation fluids, because the formation sand which flows with the production fluid is largely trapped in the interstices of the gravel.
One specific type of gravel pack procedure is called a squeeze gravel pack. The squeeze gravel pack method uses high pressure to "squeeze" the carrier fluid into the formation, thereby placing gravel in the perforation tunnels of a completed well and the screen/casing annulus. The frac pack method is very similar, except the "squeeze" is carried out at even higher pressures with more viscous/heavier fluid in order to fracture the reservoir rock. Consequently, the downhole assembly used for these two procedures is frequently the same.
Typical gravel pack or frac pack assembly is presently run into the well on a work string. The work string is a length of drill pipe normally removed from the well once the packing job is complete. The work string assembly also contains a setting tool for the packer and a crossover tool to redirect the treatment from within the work string into the formation. This assembly usually requires a setting ball to be dropped from the surface which must fall to a seat on the assembly. The setting ball actuates the setting tool and "sets" the packer, thus isolating the assembly from the upper wellbore. In some applications it establishes the crossover in the crossover tool as well. It sometimes occurs in these prior art applications that the ball is lost or damaged. Seat damage and/or debris may also cause seating problems. Further, it takes time for the ball to fall. Most importantly, the setting and crossover tools must be pulled from the well before the seal assembly and tubing may be run. This means the entire work string is removed from the well and a separate production string, through which the production fluids or gases will flow, is then landed back in the well. All this takes considerable rig time and adds to the expense of the completion. This additional time may also expose the well to fluid losses and result in formation damage. Rental and redress fees are usually charged for the use of these tools which adds to the expense of the job.
A need exists, therefore, for a gravel pack, frac pack and like assembly systems that can be run into the well on a work string that will also act as the production string (a "one-trip" assembly). This would eliminate the need for a separate work string to be run in and out of the well and save considerable rig time while greatly reducing sealing problems encountered under the present art.